I believe HSMs can model this, but don't quote me. :)

Yes, of course in theory nested state machines should be able to model this. I feel like adding more complexity and bending the rules is a bit of a concession.

Back in the days we implemented HSM helper classes in about 500 LoC and generated them from Enterprise Architect. No need to write a GUI yourself, but better to have a visual for documentation and review. Worked very well until we replaced EA with docs-as-code, now I miss that there is no nice simulator and Modeler for that workflow.

State machines don't have a native syntax in C++ at all, so you can structure them however you want. It's easy to structure a state machine, if needed, so that all (or some) states can handle the same event in the same way.

I always thought this framework was neat: https://doc.qt.io/qt-5/statemachine-api.html

Downside of course is now you have a dependency on qt.

The downside is that you're now heap allocating at least one object for every state, and I'm willing to bet that each QState has an associated std::vector-style list of actions, and that each action is also its own object on the heap.

If you can afford to do things like this you can most likely use something other than C++ and save yourself a lot of headaches.

> If you can afford to do things like this you can most likely use something other than C++ and save yourself a lot of headaches.

Surely you can understand that, despite the recent c++ hate, my job doesn't give a fuck and we aren't migrating our massive codebase from c++ to... anything.

Switch + goto is very close to being a native syntax for state machines. It's also very efficient.

goto is exactly this feature.

> State machines don't have syntax for "transition here when event is encountered no matter what state you are in" so the whole diagram becomes a spaghetti mess if you have a lot of those escape hatches.

I place a note at the top of my diagrams stating what the default state would be on receipt of an unexpected event. There is no such thing as "event silently gets swallowed because no transition exists", because, in implementation, the state machine `switch` statement always has a `default` clause which triggers all the alarm bells.

Works very well in practice; I used to write hard real-time munitions control software for blowing shit up. Never had a problem.

> hard real-time munitions control software for blowing shit up. Never had a problem.

Ha, Ha, Ha! The juxtaposition of these two phrases is really funny. I would like to apply for a position on the Testing team :-)

> Ha, Ha, Ha! The juxtaposition of these two phrases is really funny. I would like to apply for a position on the Testing team :-)

It had its moments: used to go to a range where we'd set off detonators. Once or twice in production on site where we'd set off actual explosives.